What is Resveratrol?
Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural compound found in red grape skin, Japanese knotweed (polygonum cuspidatum), peanuts, blueberries and some other berries. It is a powerful antioxidant produced by some plants to protect them against environmental stresses. Antioxidants neutralize free radicals, which are believed to be the cause of aging. Japanese knotweed is the plant source with the highest resveratrol content.
A large amount of resveratrol is produced in the skin of grapes to protect the plant against fungal diseases and sun damage; therefore wine has higher levels of resveratrol compared to other natural food. Overall, red wine contains small amounts of resveratrol, less than 1 to 2 mg per 8 ounces of red wine. However, red wine has more resveratrol than white wine because red wines are fermented with the grape skins longer than white wines. Hence, many of the antioxidants including resveratrol that are naturally present in the grape skins are extracted into the wine. Resveratrol is also present in the seeds and pomace of grapes.
Grapes grown in humid environments tend to have more resveratrol than grapes grown in more arid environments. The theory behind this phenomenon is that grapes grown in humid environments produce more resveratrol in order to fight damaging fungus (i.e. grapes grown in arid environments do not need to produce as much resveratrol to survive).
Resveratrol has been hypothesized to be responsible for low rates of heart disease in the French population compared to other populations, in spite of the fact that they have many risk factors including a high fat diet, smoking and consumption of high amounts of coffee. All of these are known contributors of high cholesterol, high blood pressure, stroke and heart attacks. In theory, this benefit in the French population is due to the consumption of moderate amounts of red wine, which is a source resveratrol. Other ingredients in wine or other factors may contribute to longevity seen in the French.
Resveratrol is available as dietary supplements from red wine extracts, grape seed extracts and Japanese knotweed extracts among others. Most supplements on the market are derived from Japanese knotweed because this plant has one of the highest concentrations of resveratrol found in nature.
The amount and purity of resveratrol in supplements can vary widely. Micronized resveratrol is available in pill or powder form. Resveratrol has low systemic bioavailability and is not well-absorbed orally. The process of micronization greatly reduces the average particle size of a compound and increases absorption.
Resveratrol is also available in solution form and as a transdermal patch. Resveratrol is considered a dietary supplement and it’s safety and effectiveness have not been approved by the US Food and Drug Administration.
How does Resveratrol work?
Resveratrol protects a cell's DNA. It is a powerful antioxidant. Antioxidants can help prevent cell damage caused by free radicals. Free radicals are unstable atoms caused by pollution, sunlight and our bodies natural burning of fat that can lead to cancer, aging and brain degeneration.
What are the benefits of taking Resveratrol?
Resveratrol has been promoted to have many health benefits such as protecting the heart and circulatory system, lowering cholesterol, and protecting against clots which can cause heart attacks and stroke. Animal studies have suggested it can lower blood sugar levels. Because resveratrol is considered an antioxidant, it is often promoted to reduce the incidence of various cancers. Animal studies also suggest resveratrol may lower brain plaque levels in Alzheimer’s disease. However, well-controlled, human clinical trials are lacking in all of these areas and many of the resveratrol claims are based in animal studies in mice. Resveratrol is considered a dietary supplement and is not approved by the U.S. Food and Drug Administration for any indication. Definitive studies demonstrating appropriate doses, uses, long-term safety and effectiveness have not been conducted.
However, the clinical utility of resveratrol in humans is under investigation. Animal studies in mice suggest there might be benefits of weight loss, reduction in insulin resistance, and reducing mortality in diabetes. Anti-cancer effects have been demonstrated in animals models, as well. Human research with resveratrol is limited. A small and brief randomized, double-blind, cross-over study in the November 2011 issue of Cell Metabolism demonstrated that 150 mg of resveratrol once daily for 30 days significantly lowered mean systolic and arterial blood pressure, tumor necrosis factor (a marker of inflammation), plasma glucose and insulin concentrations, and plasma triglyceride concentrations, among other findings. Adverse reactions to resveratrol were not seen in the study. Researchers note that longer studies at higher doses are required before results can be confirmed.
What other drugs will affect Resveratrol?
Drug interaction studies with resveratrol have not been conducted. The probable interaction with blood thinners should be taken into consideration. Patients taking blood thinning medications such as aspirin, warfarin, or clopidogrel should advise their doctor that they are taking resveratrol. Additionally, patients should always inform their health care providers of any dietary supplements or over-the-counter medications they use.
Who should not take Resveratrol?
Patients who have blood disorders, which can cause bleeding, should be monitored by a physician while taking this product. People undergoing surgery should stop taking resveratrol two weeks before the surgery and not take it for two weeks after the surgery to reduce the risk of bleeding.
Do not take resveratrol supplements or excessive amounts of natural foods containing resveratrol while pregnant or breast-feeding. There is a lack of research in this area to prove safety. Resveratrol should be avoided in children.
Resveratrol has mild estrogenic activity and until more is known, women with cancers and other conditions that are estrogen sensitive should seek medical advice before taking resveratrol.
Resveratrol reduces the activity of enzymes involved with drug metabolism but whether it has a significant effect in humans has not been studied.
What are the possible side effects of Resveratrol?
Adverse effects of resveratrol in humans have not been reported. Long-term side effects are not known. A small and brief clinical trial conducted in 2011 in obese patients given 150 mg per day of resveratrol noted no adverse reactions.
 Timmers S., Konings E., Bilet L, et al. Calorie Restriction-like Effects of 30 Days of Resveratrol Supplementation on Energy Metabolism and Metabolic Profile in Obese Humans. Cell Metabolism 2011;14: 612-622